1. Field of the Invention
The present invention relates to a deflection yoke for use in a color cathode-ray tube for forming a multiplicity of electron beams in an inline array and more particularly, to a deflection yoke having a convergence correcting means.
2. Description of the Related Art
An example of known deflection yokes having a convergence correcting means is disclosed, e.g., in JP-A-6-125474, in which a vertical deflection coil comprises a pair of coil halves each of which has a centertap and thus has first and second coil parts divided, the first coil parts of the pair of coil haves are connected at their coil ends to each other, a shunt circuit which impedance varies with a voltage between these centertaps of the coil halves is connected in parallel between the centertaps to thereby correct horizontal line misconvergences of upper and lower parts of a display screen.
In such a prior art, however, since the first and second coil parts are not separated from each other but connected to each other at their coil ends of the first coil parts of the coil half pair, when a current flowing through the shunt circuit connected between the centertaps is arranged to be passed through a correction coil to correct vertical line misconvergences of upper and lower ends of the display screen caused by the correction of the horizontal line misconvergences of the upper and lower parts of the screen, a current similar to the vertical deflection current cannot be made to flow through the correction coil.
This can be attained by providing a vertical auxiliary deflection coil for causing the current similar to the vertical deflection current to flow through the correction coil, but this disadvantageously requires a large space necessary for winding the auxiliary deflection coil around a subcore.
Further, since the winding position of the first coil part cannot be freely selected, there is another problem that the vertical line misconvergences caused by the correction of the horizontal line misconvergences of the screen upper and lower parts becomes larger at the upper and lower parts of the screen left and right ends than the vertical line misconvergences at the upper and lower parts of the screen central area.
Furthermore, since the shunt circuit, which impedance varies with the voltage appearing across the centertaps, is made up of only diodes which are conducted when subjected to a predetermined voltage or a higher voltage, left/right pincushion distortion can be corrected only at the screen upper and lower parts but remains in the screen central zone, which disadvantageously results in that left/right distortion performance is deteriorated.
In addition, for the purpose of adjusting the correction amount of the vertical line misconvergences of the screen upper and lower parts, this requires provision and adjusting operation of separate variable resistors for the respective upper and lower parts.